Hexagonal SBA-15 Research Articles

Immunoassay channels for α -fetoprotein based on encapsulation of biorecognition molecules into SBA-15 mesopores

A novel immunoassay channeling sensor for α-fetoprotein (AFP) was proposed by incorporating biorecognition molecules into the mesopores of well-ordered hexagonal SBA-15. As the biosensing element, alkaline phosphatase (ALP)-labeled antibody was embedded into the mesopores with the substrate of 1-naphthyl phosphate (1-NP). The encapsulated ALP-labeled antibody retained its bioactivities on catalytic hydrolysis reaction with 1-NP and immunological reaction with antigen. Ionic liquid–chitosan hybrid was chosen to increase film adherence and prevent the leakage of the immobilized molecules. The peak current responses decreased due to the increasing spatial blocking and impedance from the formation of nonconductive immunoconjugates on the surface of the electrode. The experimental parameters were optimized including the concentrations of the immobilized 1-NP and ALP-labeled antibody, and the amounts of SBA-15 and ionic liquid for the electrode modification. Under the optimized conditions, the constructed immunosensor could detect AFP in a linear range from 1.0 to 150 ng mL −1 with a detection limit of 0.8 ng mL −1. It provided an alternative strategy for the detection of antigens or other proteins by the mesoporous materials.

Synthesis of Spherical SBA-15 Particles under Mixed and Dilute Electrolyte Conditions

Spherical SBA-15 particles were synthesized by co-addition of dilute but strong electrolytes (NH4F and Cu(NO3)2) under classical acidic conditions without an organic solvent or another template. These materials were characterized by low angle X-ray diffraction (XRD), N2 sorption isotherms, and scanning electron microscopy (SEM). Separated uniform hexagonal SBA-15 particles form in strong acidic media while an appropriate content of fluoride anions favors the synthesis of a sphere-like and highly pored ordered structure. Effects of different electrolytes on the morphology and the mesostructure of the resulting materials were discussed. We found that fluoride played the main role in the formation of sphere-like SBA-15 while the presence of the Cu2+ was beneficial for the formation of separated spherical SBA-15 particles. When the concentration of Cu2+ increases, a part of the silica does not contribute to the formation of SBA-15. This phenomenon is probably due to the formation of a PEO (polyoxyethylene)/Cu2+ head-group at the hybrid interface which affects the normal coordination and condensation of the silica source.

Large-pore mesoporous silica with three-dimensional wormhole framework structures

Large-pore mesoporous silica with 3D wormhole framework structures (denoted MSU-J) are prepared through a supramolecular hydrogen-bonding assembly pathway from low-cost sodium silicate as the silica source and commercially available mono- and tri-amine Jeffamine and Surfonamine surfactants as structure-directing porogens. The calcined mesostructures exhibit large pore sizes (up to 8.2 nm), surface areas (632–1030 m 2/g) and pore volumes (0.5–2.0 cm 3/g), depending on the surfactant chain length and synthesis temperature (25–65 °C). The textural properties of these new wormhole mesostructures are comparable to those of hexagonal SBA-15 derivatives and large pore MCM-48. However, unlike the SBA-15 structure type, wherein the 3D pore network is formed by connecting 1D cylindrical mesopores through micropores, MSU-J mesophases have wormhole framework structures containing fully interconnected 3D mesopores that can minimize the diffusion limitations often encountered in adsorption and chemical catalysis. Also, unlike large pore MCM-48, which requires cost-intensive tetraethylorthosilicate as a silica source and the use of a co-surfactant as a pore expander under strong acid conditions, MSU-J mesostructures are assembled from low-cost sodium silicate in the presence of a single Jeffamine or Surfonamine porogen at near-neutral pH.

Synthesis of Nanowire and Hollow LiFePO4 Cathodes for High-Performance Lithium Batteries

The synthesis of nanowire and hollow LiFePO4 cathodes using the hard templates KIT-6 and SBA-15 is reported for high-performance lithium batteries. The two-dimensional hexagonal SBA-15 silica template with P6mm symmetry is used for the template that contains parallel cylindrical pores arranged with hexagonal symmetry, which serves to organize the wires into parallel bundles. On the other hand, three-dimensional cubic arrangement of pores in KIT-6 silica with Ia3d symmetry yields hollow morphology with mesopores. After impregnation of the template into a solution or after coating on the template with a solution consisting of LiFePO4 precursors, the silica template is removed and is subsequently fired at 700 °C. Electrochemical cycling of both the nanowire and hollow LiFePO4 cathodes demonstrates excellent rate capability even above 10C rate, showing >89% capacity retention of the initial capacity. Among them, the rate capability of the hollow cathode at 15C is higher than that of the nanowire cathode, show...

Synthesis and Magnetic Investigation of Ordered Mesoporous Two-Line Ferrihydrite

We report here for the first time on the synthesis and characterization of ordered mesoporous two-line ferrihydrite. Ordered mesoporous ferrihydrite has been prepared via the nanocasting route. Two types of ordered mesoporous silica, two-dimensional hexagonal SBA-15 and three-dimensional cubic KIT-6, were employed as hard templates. The magnetic behavior of ferrihydrite replicas with an average diameter of about 7 nm was investigated by direct current magnetometry. The temperature dependence of magnetization shows a superparamagnetic transition around 70 K. Field-induced changes in the low-field behavior of the magnetization were observed below 30 K. The results are explained assuming a spin-glass-like state of the surface spins. The 2D hexagonal two-line ferrihydrite showed very large coercivity up to 1.6 kOe at 5 K.

The search of promoters for silica condensation and rational synthesis of hydrothermally stable and well ordered mesoporous silica materials with high degree of silica condensation at conventional temperature

Silica samples condensed at acidic, neutral and alkaline media in the presence of various inorganic anions have been carefully investigated by 29Si MAS NMR spectroscopy. The results show that SO 4 2 - and CO 3 2 - could effectively improve the degree of silica condensation under neutral and alkaline media. Accordingly, for example, it is designable to synthesize hydrothermally stable and well ordered hexagonal mesoporous SBA-15 with very high degree of silica condensation in the presence of sulfate and carbonate species under neutral condition. As we expected, hexagonal mesoporous silica materials in the presence of sulfate (SBA-15-S) and carbonate species (SBA-15-U) show high degree of silica condensation, giving Q 4/ Q 3 ratios at 6.3 and 4.3, which are much higher than that of conventional SBA-15 ( Q 4/( Q 3 + Q 2) ratio at 1.8) synthesized in the absence of sulfate and carbonate species. Very interestingly, hexagonal mesoporous SBA-15-S and SBA-15-U shows very high hydrothermal stability, compared with SBA-15. For example, after being treated in 100% steaming at 780 °C for 3 h, SBA-15-S still remains its mesostructure. In constrast, SBA-15 loses most of the mesostructure. Furthermore, heteroatoms-substituted mesoporous materials such as aluminosilicate (Al-SBA-15-U) could also be synthesized in the presence of urea under neutral condition, and Al-SBA-15-U exhibits extraordinary hydrothermal stability. The unique and novel route for syntheses of hydrothermally stable and well ordered mesoporous silica and aluminosilicate materials in the presence of sulfate and carbonate species would be very important for potential application of mesoporous silica (SBA-15) and aluminosilicate materials (Al-SBA-15) as industrially supports and acidic catalysts.

Interaction of Nitrates with Pluronic Micelles and Their Role in the Phase Formation of Mesoporous Materials

The addition of NaNO3 to the reaction mixture of hexagonal SBA-15 changes the product to a Ia3d cubic phase. To understand the specific action of the salt, electron-spin echo envelope modulation (ESEEM) spectroscopy was applied. It allowed us to follow the local concentration of the individual ions within the micelles through their dipolar interaction with spin probes introduced into different regions of the Pluronic P123 (PEO20PPO70PEO20) micelles. The 15N and 23Na modulation depth probed the local concentration profile of the anions and cations, and the water content in these regions was followed through the modulation depth of 2H in D2O solutions. The ions were found to penetrate the hydrophilic corona region (the polyethylene oxide, PEO) of the micelles, concomitant with penetration of water molecules, reaching saturation at a bulk NaNO3 concentration of 0.2 M. In acidic micellar solutions, protons repel the Na+ ions from the corona and for the same total [NO3-] the acidity increases the NO3- capacit...

CoMo/Ti-SBA-15 catalysts for dibenzothiophene desulfurization

With a view to reducing the sulfur content in diesel fuels, novel desulfurization CoMo catalysts were supported on a Ti-loaded hexagonal mesoporous SBA-15 material. The Ti-SBA-15 substrates were synthesized using triblock copolymers as structure-directing agents. Catalytic activity was assessed in the model reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT), carried out in a batch reactor at T = 623 K and with a total hydrogen pressure of 3.1 MPa. The reaction proceeds via the direct desulfurization route (main route) and the hydrogenation (HYD) pathway. The incorporation of Ti into the SBA-15 afforded catalysts that were more active than the Ti-free counterpart, due to the enhancement of the DDS route in this reaction. This difference was explained in terms of a larger number of coordinately unsaturated sites (CUS) of the metal sulfide on Ti-loaded catalysts. Under steady-state conditions, the CoMoST20 catalyst with a Si/Ti ratio of 20 was the most active among the catalysts studied. Since this catalyst exhibited both Ti 4+ ions incorporated into the SBA-15 framework and separate anatase TiO 2 clusters located on its surface, the activity enhancement on this sample was explained by the larger intrinsic activity of the “Co–Mo–S” phase located on these TiO 2 nanoparticles. The Ti-SBA-15 supports and the CoMo/Ti-SBA-15 catalysts were studied by N 2 adsorption–desorption isotherms, XRD, TEM, FTIR of adsorbed pyridine and NO, UV–vis DRS, TPR, micro-Raman and XPS spectroscopy.

Hard Templating Pathways for the Synthesis of Nanostructured Porous Co3O4

The present study is concerned with the nanocasting preparation of Co3O4 nanostructures employing two-dimensional (2D) hexagonal SBA-15 and three-dimensional (3D) cubic KIT-6 as hard templates. The...

Encapsulation of direct blue dye into mesoporous silica-based materials

Mesoporous hexagonal silica CMI-1, MCM-41, SBA-15 and Al-incorporated silica AlCMI-1 with pore sizes of 2, 2.7, 3.8 and 3.6 nm, respectively, have been synthesized and used as host materials for the fabrication of optical materials by the encapsulation of direct blue 71 dye. The surface silanol groups of these mesoporous silicas were functionalized by silylation with 3-(aminopropyl)-triethoxysilane or methyltrimethoxylsilicate, which allow a successful doping of organic dye molecules. X-ray diffraction, N 2 adsorption, thermogravimetric analysis, infrared, UV–vis diffuse reflectance and solid-state NMR spectroscopy were used to structurally characterize these composite products. It is found that the dye molecules of direct blue 71 have been encapsulated in the pores of MCM-41, SBA-15 and AlCMI-1, whereas attached on the external surface of CMI-1. The steric effect from the pore size of the host materials is significant. Moreover, Al-species in the AlCMI-1 were believed to take an important role in the dye encapsulation, resulting in a larger blue-shift of 21 nm than other mesoporous dye/silica composites.

Controlling thickness in hexagonal polymer templated mesoporous silica films

Many templated mesoporous silica films are synthesized through a solution phase co-assembly process involving association of surfactants or block-copolymers with silica precursors that is driven by the evaporation of solvent. During the film formation, a liquid crystal type structure with well-defined nanometer scale periodicity is formed and then made rigid by condensation of the silica precursors. For a variety of applications there is an interest in controlling the film thickness. The objective of this investigation is to find systematic rules that determine film thickness in hexagonal SBA-15 type silica/polymer composite materials. We find that despite the complex self-organization in these materials, all thickness data can be fit with classic models for evaporation induced deposition in dip-coated films. The models relate film thickness, pull rate, solution viscosity, and solution density. The thickness data can be modeled with no adjustable parameters over more than an order of magnitude thickness range.

Adsorption of aqueous alkylphenol ethoxylate surfactants by mesoporous carbon CMK-3

Mesoporous carbon, CMK-3, was prepared using hexagonal SBA-15 mesoporous silica as the template and the adsorption of nonylphenol ethoxylates (NPE) onto CMK-3 was investigated. The adsorption process was well described using pseudo-second-order kinetics. At initial NPE concentrations of 107 and 530 mg l −1, the adsorption rate constants were found to be 5.6 × 10 −3 and 8.7 × 10 −4 g mg −1 min −1 , indicating that a higher initial concentration or adsorption amount resulted in a lower adsorption rate. NPE adsorption onto CMK-3 fitted a Langmuir–Freundlich model and the maximum amounts of NPE absorbed at 15, 25, and 35 °C were 923, 720, and 463 mg g −1, suggesting an elevated adsorption capacity of CMK-3 for NPE with decreased adsorption temperature. In addition, increasing adsorption temperature led to the change of the adsorption model from the Langmuir–Freundlich to the Langmuir model. N 2 adsorption results showed that the adsorption of NPE led to a decrease in the mesopore volume of CMK-3. However, the pore width of NPE-loaded CMK-3 was found to be identical to that of CMK-3.

Resolving Intermediate Solution Structures during the Formation of Mesoporous SBA-15

The evolution of the solution microstructures during the formation of the hexagonal mesoporous material SBA-15 was studied by direct imaging and freeze-fracture replication cryo-TEM. A reaction mixture was sampled at different times after the addition of tetramethoxyorthosilane (TMOS) to an acidic solution of Pluronic P123 held at 50 degrees C. Solution microstructures were detected by direct imaging cryo-TEM in the time window of 6.5-40 min after the addition of the TMOS (t = 0). The micrographs revealed that the initial spheroidal micelles evolve into threadlike micelles, which become longer and straighter with time. Then bundles with the dimensions similar to those found in the final material appeared, although there was no sign of a hexagonal arrangement up to 40 min. Due to the appearance of a precipitate at 40 min the sample became too viscous, preventing clear observation of its content. To observe the structures present after 40 min, freeze-fracture replication was carried out as well. Such samples were collected also at 22 min and showed the presence of threadlike micelles in agreement with the direct imaging cryo-TEM micrographs. The 2 h samples showed some areas of hexagonal ordered structures, which become very clear at 2 h 50 min. The cryo-TEM measurements were carried out under the same reaction conditions used in earlier in situ EPR experiments, thus allowing us to correlate molecular level events with the microstructure shape evolutions. This showed that the elongation of the micelles is a consequence of a reduction of the polarity and the water content within the micelles due to silicate adsorption and polymerization. Similar experiments were carried out also on SBA-15 prepared with HCl and TMOS at 35 degrees C. The appearance of threadlike micelles, followed by clustering of the TLMs, was observed under these conditions as well, but the reaction rate was faster. This suggests that the observed mechanism for the formation of SBA-15 is general.

Characterization of the Initial Stages of SBA-15 Synthesis by in Situ Time-Resolved Small-Angle X-ray Scattering

The initial stages of SBA-15 synthesis have been studied by using in situ time-resolved small-angle X-ray scattering with a synchrotron radiation source. The quantitative analysis of X-ray scattering and diffraction intensities allows the structures of intermediates to be identified at the different stages of SBA-15 synthesis. Following tetraethylorthosilicate (TEOS) addition, an intense small-angle scattering and an associated secondary maximum are observed, which are attributed to non-interacting surfactant template micelles encrusted with silicate species. After 25-30 min of the reaction, the broad scattering disappears and narrow Bragg diffraction peaks typical of hexagonally ordered structure are observed. The cylindrical micelles identified from X-ray scattering data appear to be the direct precursors of 2D hexagonal SBA-15 structure. Just after the formation of the SBA-15 hexagonal phase, the cylindrical micelles are only weakly linked in the hexagonal structure. As the synthesis proceeds, the solvent in the void volume between the cylindrical micelles is gradually replaced by more dense silicate species. The unit cell parameter of SBA-15 is progressively decreasing during the SBA-15 synthesis, which can be related to the condensation and densification of silicate fragments in the spaces between the cylinders. The volume fraction of the 2D hexagonally ordered phase is sharply growing during the first 2 h of the reaction. The inner core radius of SBA-15 material remains almost constant during the whole synthesis and is principally affected by the size of the poly(propylene oxide) inner core in the original cylindrical micelles.

Formation of nanosized zirconia-supported 12-tungstophosphoric acid in mesoporous silica SBA-15: A stable and versatile solid acid catalyst for benzylation of phenol

A nanosized zirconia-supported 12-tungstophosphoric acid (TPA) in SBA-15 composite was prepared by wet impregnation of TPA/ZrO 2 nanoparticles inside the mesoporous channels of SBA-15. The resulting composite material was calcined at 1123 K and characterized by elemental analysis, powder X-ray diffraction, nitrogen adsorption isotherms, transmission electron microscopy (TEM), scanning electron microscopy (SEM), solid-state 31P CP-MAS NMR, 29Si MAS NMR, UV–vis diffuse reflectance spectra, FTIR, TPD of ammonia, FTIR pyridine adsorption, and thermogravimetric analysis (TG-DTG). The synthesized TPA/ZrO 2/SBA-15 showed a well-ordered hexagonal mesoporous structure and mesoporous support SBA-15 stabilized ZrO 2-t (tetragonal) phase with crystal size in the range of 3–4 nm. SBA-15 was a better support than MCM-41 and MCM-48 because it retained its mesostructure even after high TPA loading and high calcination temperatures. Mesoporous silica support plays an important role in stabilizing the catalytically active tetragonal phase of zirconia, which gave the most active catalysts. The catalysts were examined for their catalytic activities in the liquid phase benzylation of phenol with benzyl alcohol and the catalyst 15 wt% TPA/22.4 wt% ZrO 2/SBA-15 calcined at 1123 K was found to have high acidity and to be 10 times more active than neat TPA/ZrO 2 under the reaction conditions studied in benzylation of phenol.

Adsorption of l-histidine over mesoporous carbon molecular sieves

Mesoporous carbon, CMK-3, was prepared by large pore hexagonal mesoporous silica SBA-15. The structural order and textural properties of all the materials were studied by XRD, HRTEM, and nitrogen adsorption. Adsorption of l-histidine (His) over various porous adsorbents such as CMK-3, SBA-15, and activated carbon was studied from solutions with different pH. His adsorption was observed to be pH dependent with maximum adsorption near the isoelectric point of the amino acid. CMK-3 showed a larger amount of His adsorption as compared to SBA-15 and the conventional adsorbent, namely activated carbon. CMK-3 registers the total adsorption capacity of ca. 1350 μmol g −1 which is ca. 12 times higher than the adsorption capacity of SBA-15. This large difference could be mainly due to the stronger hydrophobic interaction between the non-polar side chains of amino acids and the hydrophobic surface of the mesoporous carbon as compared to mesoporous silica. The influence of ionic strengths on the adsorption of His was also studied and the results are discussed. Nitrogen adsorption of CMK-3 after His adsorption confirmed that His molecules are tightly packed inside the mesopores.

Direct Synthesis of Well-Ordered and Unusually Reactive FeSBA-15 Mesoporous Molecular Sieves

Large-pore hexagonal SBA-15 molecular sieves partially substituted with iron(III) have been synthesized for the first time in highly acidic media. The degree of iron(III) incorporation into SBA-15 can easily be controlled by a simple adjustment of the molar ratio of water and hydrochloric acid. All the materials have been characterized by XRD, N2 adsorption, UV−Vis DRS, ESR, and XANES spectroscopy. The characterization of the FeSBA-15 materials by UV−Vis DRS, ESR, and XANES spectroscopies suggests that the iron atoms are highly dispersed and mostly occupy isolated tetrahedral sites. XANES studies revealed that the proportion of tetrahedrally coordinated Fe atoms decreases with decreasing nSi/nFe ratios. Benzylation of benzene (or substituted benzenes) using benzyl chloride as the alkylating agent over FeSBA-15 with different nSi/nFe ratios was investigated as was the same reaction using AlSBA-15 as catalyst. The influence of parameters such as reaction temperature, reactant feed ratio, and the presence of...

Nanocasting, templated syntheses and structural studies of manganese oxide nanoparticles nucleated in the pores of ordered mesoporous silicas (SBA-15)

We have used 2D hexagonal SBA-15 silicas as templates for the nanofabrication of Mn oxide particles. Despite challenging aspects (several oxidation states of manganese, several polymorphs for each oxidation state), manganese oxides were chosen because of the high economical and environmental significance associated with their ion-exchange, molecular adsorption, electrochemical, magnetic and catalytic properties. We show that single phase MnO x nanoparticles can be prepared within SBA-15 mesopores. The interest of diffraction and absorption measurements recorded in situ upon calcination to follow the crystallization of these particles at increasing length scales is illustrated. To cite this article: V. Escax et al., C. R. Chimie 8 (2005).

Assembly of Large-Pore Silica Mesophases with Wormhole Framework Structures from α,ω-Diamine Porogens

Large-pore mesoporous silicas with wormhole framework structures have been assembled through hydrogen-bonding pathways from sodium silicate or tetraethyl orthosilicate (TEOS) as the silica source and amine-terminated Jeffamine surfactants of the type H2NCH(CH3)CH2[OCH2CH(CH3)]xNH2 as the structure-directing porogen. Depending on the molecular weight of the α,ω-diamine surfactant (x ∼ 33 and 68 for Jeffamine D2000 and D4000, respectively) and the synthesis temperature (25−65 °C), the mean pore size distributions of the mesostructured silicas (denoted MSU-J) were centered between 4.9 and 14.3 nm, making these materials comparable to hexagonal SBA-15 mesostructures in average framework pore size. In addition to the BET surface areas of MSU-J silicas (408−1127 m2/g) being comparable to those of SBA-15 (630−1040 m2/g), MSU-J silicas exhibit larger pore volumes (1.37−2.29 cm3/g) than SBA-15 silicas (0.56−1.23 cm3/g) prepared in the absence of mesitylene. MSU-J wormhole mesostructures represent the largest pore sizes observed to date for a fully three-dimensional mesoporous framework assembled from a single micellar porogen. Only mesostructured micellar foam structures exhibit larger pore sizes, but the preparation of foam structures requires the use of more complex microemulsions or latex polymers as porogens.

Composite mesostructures by nano-confinement

In a physically confined environment, interfacial interactions, symmetry breaking, structural frustration and confinement-induced entropy loss can play dominant roles in determining molecular organization. Here we present a systematic study of the confined assembly of silica-surfactant composite mesostructures within cylindrical nanochannels of varying diameters. Using exactly the same precursors and reaction conditions that form the two-dimensional hexagonal SBA-15 mesostructured thin film, unprecedented silica mesostructures with chiral mesopores such as single- and double-helical geometries spontaneously form inside individual alumina nanochannels. On tightening the degree of confinement, a transition is observed in the mesopore morphology from a coiled cylindrical to a spherical cage-like geometry. Self-consistent field calculations carried out to account for the observed mesostructures accord well with experiment. The mesostructures produced by confined syntheses are useful as templates for fabricating highly ordered mesostructured nanowires and nanowire arrays.